This invention relates to inhibiting the oxidation of polymers. In particular, it relates to the use of certain non-phenolic antioxidants for that purpose.
Phenolic compounds are one of the most important classes of antioxidants used in formulating polymers, especially poly(vinylchloride) (PVC). Typical examples of such compounds include butylated hydroxytoluene (BHT), bisphenol A, and pentaerythritol tetrakis(3,5-di-ter-butyl-4-hydroxyhydrocinnamate). However, these materials can adversely affect certain polymer properties in specific applications, such as the color stability of radiation-sterilized articles.
U.S. Pat. No. 4,082,716 adds phthalide to polypropylene to improve impact and flow properties, but it discolored the polymer, which was undesirable. U.S. Pat. No. 1,941,474 adds phthalide to polyesters as plasticizers. Phthalide is 1(3H)-isobenzofuranone (9Cl). It is also known as phthalide (6Cl, 8Cl); 1-phthalanone; 2-hydroxymethylbenzoic acid y-lactone; and phthalolactone. It has the registry number 87-41-2and the formula

An article by Peter Solera titled, “New Trends in Polymer Stabilization,” in the Journal of Vinyl & Additive Technology, September, 1998, Vol. 4, No. 3, pages 198 to 210, discloses the use of a benzofuranone stabilizer (FIG. 6) referred to as “L1.” That stabilizer has the formula
and the chemical name 5,7-di-t-butyl-3-(3,4-di-methylphenyl)-3H-benzofuran-2-one.